1. Field of the Invention
This invention relates generally to tape recording and/or reproducing apparatus of the type in which, during recording and reproducing operations, the tape runs about at least a portion of the periphery of a tape guide drum having a circumferential slot through which at least one rotary transducer or magnetic head projects for recording and/or reproducing signals on the tape, and the invention is more particularly directed to an improved guide assembly for establishing the path of the tape on the tape guide drum.
2. Description of the Prior Art
In existing apparatus of the above described type, for example, in existing video tape recorders, the tape guide drum is usually composed of upper and lower drum sections which are mounted on a chassis with a small gap between the drum sections to define the circumferential slot, and the recording medium, such as, a magnetic tape, is guided to and from the periphery of the tape guide drum so as to extend helically about at least a portion of the periphery where the tape covers the circumferential slot. Further, two rotary transducers or magnetic heads are mounted on the opposite ends of a rotary support arm within the drum so as to project through the circumferential slot into contact with the tape engaging the periphery of the guide drum so that, in response to rotation of the magnetic heads and advancement or running of the tape, the heads alternately scan sucessive record tracks which extend obliquely across the tape for either recording or reproducing signals in such record tracks.
Since the tape runs helically on the periphery of the tape guide drum, accurate tracking or scanning of the oblique record tracks by the rotary magnetic heads or transducers requires that the path of the tape on the guide drum be precisely maintained. If the tape on the drum deviates from the predetermined path during either recording or reproducing operations, the quality of the video or other signals reproduced from the tape is deteriorated. Usually, the helical path of the tape on the periphery of the guide drum is established by an upwardly facing, inclined shoulder projecting from the periphery of the lower drum section so as to be engageable by the lower longitudinal edge of the tape. Such upwardly facing, inclined shoulder may be defined by a radially enlarged portion of the lower drum section, or by an arcuate strip secured to, and extending along the periphery of the lower drum section. Since the width of the tape is not precisely uniform, the positioning of the lower edge of the tape has been adopted as the standard for establishing the desired helical path of the tape on the guide drum and obtaining compatibility of various tapes and various recording and/or reproducing apparatus. Of course, when the desired helical tape path is established by engagement of the lower longitudinal edge of the tape with the upwardly facing, inclined shoulder on the lower drum section, the precise positioning of the tape in the desired helical path is achieved only so long as the lower longitudinal edge of the tape is in contact with the shoulder along the full length of the latter. However, during recording and reproducing operations, the tape extending helically about the guide drum may have a tendency to move away from the guiding shoulder, for example, by reason of tension in the tape, with the result that the tape deviates from the desired path.
In order to hold the lower longitudinal edge of the tape against the upwardly facing, inclined guide shoulder on the lower drum section, it has been proposed to employ a downwardly tapering drum section so that tension in the tape will result in forces urging the tape downwardly against the guide shoulder. However, providing the peripheral surface of the upper drum section with such taper and assembling the upper and lower drum sections in the necessary precise relationship to each other are difficult and time consuming operations. Further, in tape recording and/or reproducing apparatus of the described type, horizontal runs of the tape extending to and away from the helical path of the tape on the guide drum are guided by respective tapered guide pins or rollers mounted on the chassis adjacent the guide drum and, in the case where the upper drum section is tapered for urging the tape downwardly against the upwardly facing, inclined guide shoulder, as aforesaid, the tapered guide pins or rollers have to be precisely adjusted so as to permit the tapered upper drum section to achieve the desired effect. Thus, the use of a tapered upper drum section for maintaining the tape in contact with the upwardly facing, inclined guide shoulder involves precise and time consuming adjustments in order to obtain acceptable video or other information signals.
In U.S. Pat. No. 3,261,525, it is proposed to guide the tape on the guide drum by means of rigid studs which are adjustably mounted at spaced apart locations on the upper and lower guide drum sections so as to be engageable with the upper and lower longitudinal edges of the tape running about the guide drum. In order to define the desired helical path of the tape on the guide drum, it is necessary to precisely adjust the several guide studs on the upper and lower drum sections. Apart from the time and effort involved in effecting such precise adjustments of the several guide studs, the arrangement disclosed in this patent is disadvantageous in that the engagement of both the upper and lower longitudinal edges of the tape by the rigid guide studs does not provide accommodation for the variations in the width of the tape which cannot be eliminated in the practical manufacture of the tape. Thus, if the tape being employed has a width slightly less than that for which the rigid guide studs have been adjusted on the upper and lower drum sections, then the tape is free to drift laterally between the guide studs and will not follow a precise helical path. On the other hand, if the width of the tape being employed exceeds that for which the rigid guide studs have been adjusted, then the tape will buckle or have its edges damaged by reason of the engagement of both longitudinal edges of the tape with the rigid guide studs.